Mobile communication systems were developed to provide the subscribers with voice communication services on the move. Although the mobile communication systems have evolved recently to the level of supporting high speed data communication services beyond the early voice-oriented services, resource shortages and user requirements for higher speed services are spurring evolution towards increasingly more advanced mobile communication systems.
Meanwhile, unlike voice services, data services are provided using the resources determined based on transmit data amount and channel condition. Accordingly, a wireless communication system, particularly a cellular communication system, is provided with a scheduler, which takes charge of resource allocation in consideration of the required resource amount, channel condition, data amount, etc. Typically, in most cellular communication systems the scheduler is located in base stations for radio resource management, and this is the case even in the long-term evolution (LTE) system as one of the next generation mobile communication systems.
Recently, a technique called licensed assisted access (LAA) has been proposed to improve frequency utilization efficiency by using carrier aggregation (CA) across licensed and unlicensed bands.
In an LTE system operating on a licensed band frequency, the frequency owner may use the frequency resources exclusively in the way as intended. In the case of the communication devices operating in an unlicensed band, however, they have to share a channel in the unlicensed band; thus, there is a need of a method for sharing the channel without collision. Listen before talk (LBT) is a technique for sensing a radio channel and, if the channel is not in use, starting transmission. Here, the operation of determining whether the channel is occupied by another communication device is called channel sensing or clear channel assessment (CCA).
In an LAA system, an LAA communication-enabled terminal may collect channel occupancy information including unlicensed frequency channel occupancy and channel occupancy time that are determined based on the control information received from a base station. However, certain terminals (e.g., LAAs that cannot decode the control information and wireless local area network (WLAN) terminals) cannot check the channel occupancy information contained in the control information transmitted by the base station. Accordingly, if there is any terminal performing Wi-Fi communication around the LAA terminal being served by an LAA base station, the neighboring Wi-Fi terminal is likely to cause interference to the LAA communication of the LAA terminal, i.e., hidden node problem.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.